Breakthrough Metal/Graphene Interface Phonon Engineering for Reliable Graphene Based-Heat Spreaders

Graphene is predicted to be a potential heat spreader due to its high thermal conductivity. However, the same has not been explored and demonstrated yet for such application probably due to a lack of promising thermal characterization techniques in the nanosecond time scales and for sub-mm resolution. This work, for the first time, reveals the limitations of graphene as a heat spreader despite its very high thermal conductivity by capturing the nanosecond time evolution of generated hotspots over graphene using the thermo-reflectance characterization technique. The bottleneck is because of the weak phonon coupling of graphene with metal due to the lack of interplanar acoustic phonon mode. To address the issue, this work proposes and demonstrates a unique orbital overlap engineering solution to enhance the phonon coupling of graphene with a hot spot source. The engineering solution reduces generated hotspot temperature by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">~ 2.2×</tex> and the thermal decay time constant by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">~ 1.78×</tex> for the same dissipated power. Moreover, the engineering method removes generated hotspots through fast heat spreading. Physical insights are developed using nanosecond time scale thermoreflectance characterization and DFT computations to develop guidelines for graphene-based fast on-chip heat spreaders.